Aluminum alloy sheet material and method for producing the same

ABSTRACT

An aluminum alloy sheet material, containing 2.6% by mass or more and less than 3.5% by mass (% by mass is simply denoted by % hereinafter) of Si, 0.05 to 0.5% of Mg, 0.5% or more and less than 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0% of Fe, and containing, if necessary, at least one of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2% of V, and 0.01 to 0.2% of Ti, with the balance of Al and unavoidable impurities. A method of producing the aluminum alloy sheet material, which method contains carrying out specific workings.

FIELD

[0001] The present invention relates to an aluminum alloy sheet materialand a method for producing the same.

BACKGROUND

[0002] Wrought materials using an aluminum alloy are used in many fieldsby taking advantage of its lighter weight as compared with steelmaterials. For example, in recent years, automobiles are desired to belight weight for reducing the amount of exhaust gases (to preventenvironmental pollution) and for improving fuel efficiencies,considering the effect on global environments. For attaining the aboveobjective, use of an aluminum alloy is being investigated. It is thoughtthat sheet materials using an aluminum alloy are able to be applied forvarious sheet members, such as outer materials including a hood and adoor, or inner materials of automobiles, and that they can greatlycontribute for making the body of the automobile lightweight.

[0003] Aluminum alloys of 5000-series and 6000-series are representativematerials that have been conventionally used for such the aluminum alloysheet material for automobiles. However, there are such problems forapplying these alloy sheet materials for the automobile that they are alittle inferior in mechanical strength to steel materials even by takinghardening after baking into consideration, that cracks are liable tooccur in forming with a press and the like due to inferior formabilityto other materials including steel materials, and that the material isbroken at a bending portion formed by hem-bending to bend the peripheryof the sheet material when it is used as an outer material. Sinceimpurity contents of these alloys are strictly prescribed, a virginingot of aluminum and mother alloys containing various kinds of additiveelements should be blended as raw materials for producing the sheetmaterial. Accordingly, it is difficult to use aluminum alloy scraps orsecondary ingots and the like that are supplied from markets and containa rather large amount of impurities, for applying to these sheetmaterials by re-melting them as they are, rendering them difficult forrecycling.

SUMMARY

[0004] The present invention is an aluminum alloy sheet material, whichcomprises 2.6% by mass or more and less than 3.5% by mass of Si (% bymass is simply denoted by % hereinafter), 0.05 to 0.5% of Mg, 0.5% ormore and less than 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and0.3 to 2.0% of Fe, and which comprises, if necessary, at least oneselected from the group consisting of 0.01 to 0.2% of Cr, 0.01 to 0.2%of Zr, 0.01 to 0.2% of V, and 0.01 to 0.2% of Ti, with the balance of Aland unavoidable impurities.

[0005] Further, the present invention is a method for producing analuminum alloy sheet material, which method comprises:

[0006] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, and which comprises, if necessary, at least one selected from thegroup consisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2%of V, and 0.01 to 0.2% of Ti, with the balance of Al and unavoidableimpurities;

[0007] hot-rolling the cast aluminum alloy after applying homogenizingtreatment;

[0008] cold-rolling the rolled aluminum alloy, to form a sheet thereofwith a prescribed thickness; and

[0009] subjecting the sheet to heat-treatment by holding the sheet at atemperature of 450° C. or more for a time period of 120 seconds or less,and cooling to a temperature of 100° C. or less at a cooling speed of100° C./min or more;

[0010] wherein, with respect to the aluminum alloy sheet material,tensile strength and 0.2% proof stress, when they are represented by T(MPa) and Y (MPa), respectively, satisfy conditions as shown by thefollowing formula:

T ² /Y≧350.

[0011] Further, the present invention is a method for producing analuminum alloy sheet material, which method comprises:

[0012] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, and which comprises, if necessary, at least one selected from thegroup consisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2%of V, and 0.01 to 0.2% of Ti, with the balance of Al and unavoidableimpurities;

[0013] hot-rolling the cast aluminum alloy after applying homogenizingtreatment;

[0014] cold-rolling the rolled aluminum alloy, to form a sheet thereofwith a prescribed thickness; and

[0015] subjecting the sheet to heat-treatment by holding the sheet at atemperature of 300° C. or more and 420° C. or less for a time period of30 minutes or more, and cooling to room temperature at a cooling rate of60° C./min or less;

[0016] wherein, with respect to the aluminum alloy sheet material, 0.2%proof stress is 100 MPa or less.

[0017] Further, the present invention is a method for producing analuminum alloy sheet material, which method comprises:

[0018] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, and which comprises, if necessary, at least one selected from thegroup consisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2%of V, and 0.01 to 0.2% of Ti, with the balance of Al and unavoidableimpurities,

[0019] wherein a cooling rate for solidifying a molten liquid isadjusted to 50° C./sec or more by continuous cast-rolling, in themelting and casting step.

[0020] Other and further features and advantages of the invention willappear more fully from the following description.

DETAILED DESCRIPTION

[0021] According to the present invention, there is provided thefollowing means:

[0022] (1) An aluminum alloy sheet material, comprising 2.6% or more andless than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and less than1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0% of Fe,with the balance of Al and unavoidable impurities;

[0023] (2) The aluminum alloy sheet material described in item (1),further containing a component originating from scraps of an aluminumalloy in at least a part of the sheet material;

[0024] (3) The aluminum alloy sheet material described in item (1) or(2), wherein concentrations of Si, Mn and Fe, when they are representedby A%, B% and C%, respectively, satisfy conditions as shown by thefollowing formula:

(0.015×A+0.15×B+0.03×C)≦0.445, and

[0025] wherein a density of precipitates with an average diameter of 100μm or more is 2 precipitates/cm² or less;

[0026] (4) The aluminum alloy sheet material described in item (1), (2)or (3), wherein tensile strength and 0.2% proof stress, when they arerepresented by T (MPa) and Y (MPa), respectively, satisfy conditions asshown by the following formula:

T ² /Y≧350;

[0027] (5) The aluminum alloy sheet material described in item (1), (2)or (3), wherein 0.2% proof stress is 100 MPa or less;

[0028] (6) The aluminum alloy sheet material described in item (1), (2)or (3), wherein 0.2% proof stress after baking of a coating is higher by30 MPa or more than 0.2% proof stress before baking;

[0029] (7) A method for producing the aluminum alloy sheet materialdescribed in item (4), comprising:

[0030] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, with the balance of Al and unavoidable impurities;

[0031] hot-rolling the cast aluminum alloy after applying homogenizingtreatment;

[0032] cold-rolling the rolled aluminum alloy, to form a sheet thereofwith a prescribed thickness; and

[0033] subjecting the sheet to heat-treatment by holding the sheet at atemperature of 450° C. or more for a time period of 120 seconds or less,and cooling to a temperature of 100° C. or less at a cooling speed of100° C./min or more;

[0034] (8) A method for producing the aluminum alloy sheet materialdescribed in (5) comprising:

[0035] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, with the balance of Al and unavoidable impurities;

[0036] hot-rolling the cast aluminum alloy after applying homogenizingtreatment;

[0037] cold-rolling the rolled aluminum alloy, to form a sheet thereofwith a prescribed thickness; and

[0038] subjecting the sheet to heat-treatment by holding the sheet at atemperature of 300° C. or more and 420° C. or less for a time period of30 minutes or more, and cooling to room temperature at a cooling rate of60° C./min or less;

[0039] (9) A method for producing the aluminum alloy sheet materialdescribed in (1) or (2), comprising:

[0040] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, with the balance of Al and unavoidable impurities,

[0041] wherein a cooling rate for solidifying a molten liquid isadjusted to 50° C./sec or more by continuous cast-rolling, in themelting and casting step;

[0042] (10) An aluminum alloy sheet material, comprising 2.6% or moreand less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and less than1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0% of Fe,and comprising at least one selected from the group consisting of 0.01to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2% of V, and 0.01 to 0.2%of Ti, with the balance of Al and unavoidable impurities;

[0043] (11) The aluminum alloy sheet material described in item (10),further containing a component originating from scraps of an aluminumalloy in at least a part of the sheet material;

[0044] (12) The aluminum alloy sheet material described in item (10) or(11), wherein concentrations of Si, Mn, Fe, Cr, Zr and Ti, when they arerepresented by A%, B%, C%, D%, E% and F%, respectively, satisfyconditions as shown by the following formula:

{0.015×A+0.15×B+0.03×C+0.60×(D+E)+0.50×F}≦0.445, and

[0045] wherein a density of precipitates with an average diameter of 100μm or more is 2 precipitates/cm² or less;

[0046] (13) The aluminum alloy sheet material described in item (10),(11) or (12), wherein tensile strength and 0.2% proof stress, when theyare represented by T (MPa) and Y (MPa), respectively, satisfy conditionsas shown by the following formula:

T ² /Y≧350;

[0047] (14) The aluminum alloy sheet material described in item (10),(11) or (12), wherein 0.2% proof stress is 100 MPa or less;

[0048] (15) The aluminum alloy sheet material described in item (10),(11) or (12), wherein 0.2% proof stress after baking of a coating ishigher by 30 MPa or more than 0.2% proof stress before baking;

[0049] (16) A method for producing the aluminum alloy sheet materialdescribed in item (13), comprising:

[0050] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, and which comprises at least one selected from the groupconsisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2% of V,and 0.01 to 0.2% of Ti, with the balance of Al and unavoidableimpurities;

[0051] hot-rolling the cast aluminum alloy after applying homogenizingtreatment;

[0052] cold-rolling the rolled aluminum alloy, to form a sheet thereofwith a prescribed thickness; and

[0053] subjecting the sheet to heat-treatment by holding the sheet at atemperature of 450° C. or more for a time period of 120 seconds or less,and cooling to a temperature of 100° C. or less at a cooling speed of100° C./min or more;

[0054] (17) A method for producing the aluminum alloy sheet materialdescribed in (14) comprising:

[0055] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, and which comprises at least one selected from the groupconsisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2% of V,and 0.01 to 0.2% of Ti, with the balance of Al and unavoidableimpurities;

[0056] hot-rolling the cast aluminum alloy after applying homogenizingtreatment;

[0057] cold-rolling the rolled aluminum alloy, to form a sheet thereofwith a prescribed thickness; and

[0058] subjecting the sheet to heat-treatment by holding the sheet at atemperature of 300° C. or more and 420° C. or less for a time period of30 minutes or more, and cooling to room temperature at a cooling rate of60° C./min or less; and

[0059] (18) A method for producing the aluminum alloy sheet materialdescribed in (10) or (11), comprising:

[0060] melting and casting an aluminum alloy which comprises 2.6% ormore and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and lessthan 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0%of Fe, and which comprises at least one selected from the groupconsisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2% of V,and 0.01 to 0.2% of Ti, with the balance of Al and unavoidableimpurities,

[0061] wherein a cooling rate for solidifying a molten liquid isadjusted to 50° C./sec or more by continuous cast-rolling, in themelting and casting step.

[0062] The function of each element in the aluminum alloy according tothe present invention will be described below.

[0063] The aluminum alloy according to the present invention comprises2.6% or more and less than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or moreand less than 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3to 2.0% of Fe, and comprises, if necessary, at least one selected fromthe group consisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to0.2% of V, and 0.01 to 0.2% of Ti, with the balance of Al andunavoidable impurities. The function of each element will be describedhereinafter.

[0064] Si is an element that forms an intermetallic compound Mg₂Si tocontribute in enhancing the mechanical strength when it coexists withMg. Si that forms a solid solution after melt-treatment, forms a β-phaseby conformed precipitation together with Mg after the subsequent baking,and also contributes in improving the mechanical strength after baking.However, these effects cannot be fully obtained when the content of Siis less than 2.6%. On the other hand, these effects are saturated whenthe content is 3.5% or more, in addition to reducing bending propertywhen the content of Si is too large, since the amount of elementary Sior intermetallic compounds containing Si that serves as breakageinitiation points during forming becomes too large. Accordingly, thecontent of Si is 2.6% or more and less than 3.5%, preferably in therange of 2.8 to 3.2%. The upper limit of the Si content as high asinfinitely close to 3.5% may contribute to efficient recycling of thealloy according to the present invention. That is, in the recyclingprocess of aluminum alloy scraps having a high content of Si,application fields that can use the high Si-content aluminum alloy as itis are quite restricted. As a result, the scraps have been usually usedas oxygen scavengers in the producing process of steels or scrapped asthey are, except when the scraps are used by diluting with a largequantity of virgin ingots or they are used as a part of alloys forcastings. However, the permissible range of the Si content in the alloyaccording to the present invention is so wide that it is possible to usethe scraps as they are that have been impossible to use as a wroughtmaterial in the currently applicable standard of alloys, therebyenabling the aluminum alloy to be subjected to closed recycling.

[0065] Mg contributes to enhancing the mechanical strength by formingMg₂Si as has been described with respect to Si. In addition, Mg in asolid solution also contributes to enhancing the mechanical strengthafter baking, by forming a β-phase with Si by baking. This effect cannotbe fully exhibited when the amount of addition of Mg is less than 0.05%,while a content of more than 0.5% only results in saturation of thestrength improving effect. Accordingly, the content of Mg is 0.05 to0.5%, preferably 0.1 to 0.4%.

[0066] Cu exerts a strength enhancing effect by forming a solid solutionin a matrix, as well as a formability improving effect of the sheetmaterial. A too small content of Cu makes these effects insufficient,while too much content of Cu allows these effects to be saturated whiledeteriorating casting ability to make manufacture of the ingotdifficult. Accordingly, the content of Cu is 0.5% or more and less than1.2%, preferably in the range of 0.62 to 1.1%, more preferably 0.65 to1.1%, and most preferably in the range of 0.7 to 1.1%.

[0067] Mn also serves for enhancing the mechanical strength. This effectbecomes insufficient when the Mn content is too small, while formabilitydecreases when the content of Mn is too large since giant precipitatesof Al—Mn or Al—Mn—Si—Fe compounds are occurred that serve as breakageinitiation points during the forming process. Accordingly, the contentof Mn is 0.6 to 1.5%, and preferably 0.7 to 1.2%.

[0068] Zn is also an element effective for improving the mechanicalstrength and maintaining the mechanical strength after coating/baking.This effect becomes insufficient when the content of Zn is too small,while the effect is saturated when the content of Zn is too large.Accordingly, the content of Zn is 0.5 to 1.6%, preferably in the rangeof 0.7 to 1.2%.

[0069] Fe has a function for improving toughness by making the crystalgrain fine. This effect becomes insufficient when the content of Fe istoo small, while workability decreases when the content of Fe is toolarge due to occurrence of giant precipitates. Accordingly, the contentof Fe is 0.3 to 2.0%, preferably in the range of 0.6 to 1.2%.

[0070] Adding an element selected from Cr, Zr, V and Ti makes toughnessof the resulting alloy to be improved by forming fine crystallinegrains. For example, impact energy absorbing property is improved byadding at least one of these elements in the alloy sheet material to beused as an automobile frame member, thereby contributing to protectionof drivers and walkers, and the like. However, in the case of adding atleast one of the these elements, these effects are insufficient when theamount of addition of these elements is too small, while toughnessdecreases, on the contrary, when the amount of addition is too largebecause these elements form coarse intermetallic compounds withaluminum. Therefore, the preferable amount of addition of these elementsis as described in the above.

[0071] When further improvement in press-formability, such as drawingproperty, stretch-forming property and bending property, are desirablein the present invention, it is preferable that the concentrations ofSi, Mn and Fe, as represented by A%, B% and C%, respectively, satisfyconditions of the following formula:

(0.015×A+0.15×B+0.03×C)≦0.445  (1)

[0072] or that, the concentrations of Si, Mn, Fe, Cr, Zr and Ti, asrepresented by A%, B%, C%, D%, E% and F%, respectively, satisfyconditions of the following formula:

{0.015×A+0.15×B+0.03×C+0.60×(D+E)+0.50×F}≦0.445  (2),

[0073] in addition to adjusting the composition range of each elementabove. When the concentrations of Si, Mn and Fe, and if necessary theconcentrations of Cr, Zr and Ti do not satisfy the conditions of theformulas above, a large quantity of coarse intermetallic compoundscontaining these elements as constituting components are precipitatedduring the casting step. This coarse intermetallic compound persists infinal products as it is, without any changes during the producingprocess. When the final sheet material contains a large quantity of suchintermetallic compounds, they serve as initiation pints of breakage inthe press forming and bending, to deteriorate press-formability andbending property. Accordingly, in the present invention, theconcentrations of Si, Mn and Fe, and if necessary the concentrations ofCr, Zr and Ti are preferably in the range satisfying the conditions ofany one of the formulas described above. Furthermore, the density of theprecipitates with an average grain diameter of 100 μm or more existingin the sheet material, is preferably to be 2 precipitates/cm² or less.The sheet material becomes susceptible to breakage and press formabilityor bending property is deteriorated, when the density of theprecipitates having the average diameter of 100 μm or more is higherthan 2 precipitates/cm². Therefore, the density of the precipitates withan average diameter of 100 μm or more is preferably to be 2precipitates/cm² or less.

[0074] Since the aluminum alloy according to the present invention cancontain large quantities of Si, Mn, Zn and Cu, scraps of variousaluminum alloys may be used as raw materials of the aluminum alloyaccording to the present invention by recycling. No particularrestrictions are necessary to be provided for the scraps to be used. Forexample, use can be made of various scraps obtained in machiningprocesses, such as scraps of aluminum cans (UBC), scraps of aluminumsashes, scraps of structural materials of automobiles, and other scrapsof aluminum sheet products and scraps of aluminum extrusion products. Inparticular, since a variety of aluminum alloy members, such as castingsand wrought materials, are used in automobiles, they can be subjected toclosed recycling for automobile materials, by adjusting the aluminumalloy scraps originating from automobiles to have a composition rangeaccording to the present invention, and by using the aluminum alloyobtained therefrom as sheet materials for automobiles.

[0075] In the present invention, when it is desirable to further improvethe drawing property, among various press-forming properties, thetensile strength and the 0.2% proof stress, as represented by T MPa andY MPa, respectively, preferably satisfy conditions of the followingformula (3):

T ² /Y≧350.

[0076] When this correlation formula between the tensile strength andthe 0.2% proof stress is satisfied, a sufficient forming height can beobtained, by making flow of the molten alloy into the flange part easyin drawing with a press, since a sufficient mechanical strength of thematerial is secured. The effective producing method that satisfies theconditions of the formula comprises the steps of: melting and castingthe aluminum alloy having the foregoing composition; hot-rolling thealloy after applying homogenizing treatment; cold-rolling the alloy, toform a sheet thereof with a prescribed thickness; and subjecting thesheet to heat-treatment of holding the sheet at a temperature of 450° C.or more for a time period of 120 seconds or less and then cooling thesheet to a temperature of 100° C. or less at a cooling rate of 100°C./min or more. While the upper limit of the cooling rate is notparticularly restricted, it is generally 150° C./sec or less. The lowerlimit of the holding time is also not restricted particularly, and thesheet may be cooled immediately after reaching the desiredheat-treatment temperature. The preferable upper limit of the heattreatment temperature is 555° C. or less, in order to attain asufficient supersaturating concentration of each element in the solidsolution that contributes to improvement in mechanical strength, or toobtain a sufficient mechanical strength that satisfies the aboveformula. When the holding temperature is too low or the cooling rate istoo low, an improvement in drawing property may not be expected with aninsufficient mechanical strength in some cases, since sufficientsupersaturating concentration in the solid solution cannot be obtained.When the holding time is longer than 120 seconds, the supersaturatingconcentration in the solid solution is saturated, to merely result inlow productivity. Accordingly, the producing conditions as describedabove are preferably applied for further improving drawing property inthe present invention.

[0077] In the present invention, after the above-mentionedheat-treatment, a heat-treatment for holding the aluminum alloy sheet ata temperature of 250° C. or less for a time period of 120 seconds orless can be applied, as a stabilization treatment (a restorationtreatment) for reducing the change of mechanical strength of the productwith the lapse of time.

[0078] In the present invention, the 0.2% proof stress can be increasedby applying baking finish after machining into automobile members underthe conditions as described above. This increase of the proof strengthenables the aluminum alloy sheet material according to the presentinvention to be applied to frame members that require high mechanicalstrength that cannot be attained by conventional aluminum alloys.

[0079] In the present invention, when it is desirable to further improvethe bending property and stretch forming property, the 0.2% proof stressis to be 100 MPa or less. The difference between the matrix strength andgrain boundary strength (the strength influenced by grain boundaryprecipitation or non-precipitation zones) is reduced when the 0.2% proofstress is 100 MPa or less, thereby reducing stress concentration ongrain boundaries during forming, to enable a sufficient elongationrequired for forming to be ensured. Consequently, a sufficient formingheight can be secured in stretch forming, and edges with good outerappearance can be obtained in bending without rough surfaces ascribed tolocal deformation in the vicinity of grain boundaries with no occurrenceof cracks. The producing method that satisfies the above conditionscomprises the steps of: melting and casting the aluminum alloy havingthe forgoing composition; hot-rolling the cast alloy after applyinghomogenizing treatment; cold-rolling the rolled alloy, to form a sheetof the alloy with a prescribed thickness; and subjecting the sheet toheat treatment of holding the sheet at a temperature of 300° C. or moreand 420° C. or less for a time period of 30 minutes or more and thencooling the sheet to room temperature at a cooling rate of 60° C./min orless. When the holding temperature is too low, or the holding time istoo short, or the cooling rate is too fast, sufficient drawing propertyand stretch-forming property may not be obtained in some cases.

[0080] Further, in the present invention, it is also possible to improveformability by adjusting the cooling rate in the solidifying of a moltenliquid at 50° C./min or more by a continuous cast-rolling method, whenmelting and casting the aluminum alloy having the foregoing composition.In other words, by making the molten liquid to be quenched in the abovemanner, giant intermetallic compounds may be prevented fromprecipitating even when the relation among the concentrations of Si, Mn,Fe, Cr, Zr and Ti, as represented by A%, B%, C%, D%, E% and F%,respectively, do not necessarily satisfy the conditions of the formula(1) or (2) above, thereby permitting breakage by forming ascribed to thegiant intermetallic compounds to be avoided. In addition, the cast sheetthus-obtained has an average length of the dendrite arm spacing (DAS) of18 μm or less. Since the proportion of segregation in the materialbecomes smaller as DAS is shorter, a more uniform structure of the alloycan be obtained. This effect becomes larger at the cooling rate of 50°C./sec or more during solidification by the continuous cast-rollingmethod, and a cooling rate lower then the rate above does not contributeto the improvement of formability. Accordingly, the cooling rate isgenerally 50° C./sec or more, preferably 60° C./sec or more.Specifically, this cooling rate can be attained by using a twin-roll,belt or block type continuous cast-rolling machine.

[0081] The aluminum alloy sheet material according to the presentinvention is excellent in mechanical strength, drawing property,stretch-forming property, bending property, and hardness after baking.The aluminum alloy sheet material enables wide range of aluminum alloyscraps to be used as raw materials for producing the sheet material,while being excellent in applicability for recycling and being able tosuppress the producing energy cost. The present invention makes itpossible to produce the aluminum alloy sheet material that isparticularly preferable for use in automobiles with low cost, byimproving press-formability, bending property and stretch formingproperty.

[0082] Further, the aluminum alloy sheet material of the presentinvention is improved, particularly, in press-formability (drawingproperty, stretch-forming property, bending property, and the like).

[0083] Further, the aluminum alloy sheet material of the presentinvention is improved, particularly, in bending property andstretch-forming property.

[0084] The present invention will be described in more detail based onthe example below, but the invention is not limited to those.

EXAMPLES

[0085] Table 2 shows chemical compositions of aluminum alloys to be usedin the following examples according to the present invention andcomparative examples. Based on these compositions, an aluminum ingot,and mother alloys of magnesium, zinc and other elements, or scraps of analuminum alloy were appropriately mixed and melted, and the moltenliquid was formed into an ingot with a thickness of 500 mm by a DC(Direct Chill) casting process. When it is difficult to form a molten(liquid) metal using the aluminum alloy scraps as they are, a reclaimedingot manufactured by previously melting and reclaiming the scrap alonemay be used. A continuous cast-roll coil was separately produced by thetwin-roll process by increasing the cooling rate of the molten metal.Aluminum alloys of the compositions corresponding to JIS 5052 and JIS6061, respectively, were prepared, as comparative examples. The valuescorresponding to the Cr equivalence for each composition as determinedby the following formula are also shown in Table 2:

Cr equivalence=(0.015×A+0.15×B+0.03×C),

[0086] or

Cr equivalence={0.015×A+0.15×B+0.03×C+0.60×(D+E)+0.50×F},

[0087] wherein A, B, C, D, E and F denote the concentrations of Si, Mn,Fe, Cr, Zr and Ti, respectively in mass % unit.

[0088] The scrap of the alloy that was used in the mark D in the exampleaccording to the present invention corresponds to the scrap of a castingfor machines (including those for use in automobiles) having thecomposition shown in Table 1.

[0089] The proportion to be used of the scrap of alloys was adjusted tobe about 70 percent of the total mass, and the remaining part wasadjusted with a virgin ingot and mother alloys of each element. TABLE 1Chemical composition of scrap of castings for machines (mass %) Si Mg CuMn Zn Fe Cr Zr V Ti Al 5.9 0.2 1.4 1.1 1.7 2.0 0.05 or less balance

[0090] The cast ingot by the DC casting was subjected to homogenizingtreatment, and then the resulting ingot was formed into a sheet with athickness of 3 mm by hot-rolling. Then, by cold-rolling the sheet, arolled sheet with a final thickness of 1 mm was produced. The continuouscast coil was formed into a rolled sheet with a final thickness of 1 mmby cold-rolling. These rolled sheets were heat-treated under theconditions described in Table 3. As shown in Table 3, a part of thematerials were subjected to another heat-treatment corresponding tobaking finish at 180° C. for 30 minutes, in order to confirm the degreeof hardening by baking.

[0091] The samples No. 6 and 8 in the sheet materials according to thepresent invention were cooled to room temperature at a cooling rate of50° C./min after holding the cold-rolled sheet at 400° C. for 120minutes.

[0092] The samples No. 1, 2, 3, 4, 5, 7, 9, 10 and 11 of the sheetmaterials according to the present invention were subjected to heattreatment of the cold-rolled sheet, by keeping at a temperature of 500°C. for 15 seconds, followed by cooling to a temperature of 100° C. orless at a cooling speed of 180° C./min. Other samples were heat-treatedunder the conditions shown in Table 3.

[0093] Characteristics of the thus-obtained sheet materials as describedabove were measured under the conditions below.

[0094] {Tensile Test}

[0095] The tensile strength, 0.2% proof stress and elongation weredetermined at a tensile speed of 10 mm/min using JIS No. 5 test piecesand an Instron type tensile tester. Each test sample was sampled in thedirections of 0°, 90° and 45° C. along the roll direction, and a meanvalue was calculated by averaging the measured values along therespective directions.

[0096] {Drawing Test}Each sheet was blanked with a diameter of 85 mm,and was drawn into a cylinder by applying a wrinkling press force of3,000 kgf. The height immediately after breakage by this test wasmeasured, to define the forming height by drawing.

[0097] {Stretch-forming Test}

[0098] The sheet material was fixed with a wrinkling press provided witha lock bead, and was subjected to a stretching test using a sphericalpunch with a diameter of 50 mm. The height immediately after breakagewas measured by this test, which was defined as a forming height bystretch forming.

[0099] {Bending Test}

[0100] The sheet material was processed into a JIS No. 3 bending testpiece, which was subjected to 180° and 90° bending tests, separately.The test results were evaluated as best results (⊚) when no cracks wereoccurred in the 180° and 90° bending tests, as good (◯) when cracks werenot occurred only in the 90° bending test, and as poor (x) when crackswere occurred in both of the bending tests.

[0101] It was confirmed from microscopic observations of the samples No.1 to 30 shown in Table 3 that the precipitate density with an averagediameter of 100 μm or more was 2 precipitates/cm² or less in all theexamples (Nos. 1 to 11) according to the present invention, while thedensity was 3 precipitates/cm² in Comparative example Nos. 18, 20 and 25and 4 precipitates/cm² in Nos. 22 and 26.

[0102] The results obtained in the foregoing test methods are listed inTable 3. TABLE 2 (Unit of Concentra- tion: mass %) Mark Si Mg Cu Mn ZnFe Cr Zr V Ti Al Cr Equivalence* Note Example A 2.70 0.08 0.60 0.65 0.600.33 — — — — Balance 0.148 according to B 3.10 0.30 0.80 0.95 1.00 0.650.05 0.03 — 0.10 Balance 0.307 this C 3.20 0.35 1.10 1.14 1.40 1.20 0.10— 0.06 0.08 Balance 0.355 invention D 3.44 0.46 1.12 0.90 1.55 1.80 0.030.16 0.17 0.17 Balance 0.440 Scraps of an aluminum alloy was used A13.34 0.45 0.62 0.62 0.65 0.78 0.02 — — 0.02 Balance 0.189 A2 3.35 0.440.65 0.62 0.66 0.77 0.03 — — 0.02 Balance 0.194 A3 3.35 0.45 0.70 0.620.66 0.77 0.02 — — 0.01 Balance 0.183 Comparative E 2.45 0.30 0.70 0.800.80 0.60 0.17 0.02 — 0.10 Balance 0.339 example F 3.71 0.29 0.82 1.001.10 0.80 — — — 0.03 Balance 0.245 G 3.01 0.03 0.75 0.95 0.91 0.65 — —0.05 — Balance 0.207 H 2.92 0.28 0.41 1.01 0.95 1.00 0.05 — 0.10 0.03Balance 0.270 I 3.11 0.30 1.30 0.90 1.00 0.85 — 0.10 — 0.05 Balance0.292 J 3.03 0.27 0.77 0.45 0.80 1.02 — — — 0.10 Balance 0.194 K 3.210.32 0.81 1.70 1.11 0.80 — — — — Balance 0.327 L 2.97 0.31 0.80 0.880.35 0.60 — 0.03 — 0.18 Balance 0.303 M 3.20 0.27 0.83 0.95 0.70 0.150.12 0.16 0.15 0.10 Balance 0.413 N 2.95 0.25 0.90 0.91 0.80 2.30 0.050.05 0.05 — Balance 0.310 O 3.40 0.44 1.10 1.12 1.50 1.81 0.17 0.01 0.170.15 Balance 0.456 P 0.70 1.01 0.30 0.10 0.14 0.29 — — 0.01 0.03 Balance0.049 Corresponding to JIS6061 Q 0.21 2.51 0.04 0.04 0.05 0.31 0.17 —0.01 0.02 Balance 0.130 Corresponding to JIS5052 R 3.27 0.42 1.00 1.121.45 1.78 0.16 0.01 0.16 0.16 Balance 0.452 S 3.40 0.42 0.60 1.15 1.401.77 0.18 0.01 0.15 0.15 Balance 0.466 U 2.70 0.40 0.70 0.52 0.20 0.650.05 0.03 0.03 0.03 Balance 0.201 V 2.68 0.42 1.30 0.53 0.58 0.60 0.060.02 0.02 0.03 Balance 0.201 W 2.82 0.36 0.85 0.59 1.02 0.80 0.03 — —0.02 Balance 0.183 X 3.00 0.5  0.63 0.46 1.1  0.85 0.06 — — 0.02 Balance0.186

[0103] TABLE 3 Producing Conditions Tensile Test Restoration 0.2% MarkHeat Treatment Treatment 0.2% Proof of Casting Heating Holding HoldingTensile Proof Stress Alloy Cooling Tempera- Tempera- Holding CoolingTempera- Holding Strength Stress after Elonga- Forming Height (mm)Sample to be Rate DAS ture ture Time rate ture Time [T] [Y] Baking tionstretch Bending No. used (° C./sec.) (μm) (° C./min.) (° C.) (min.) (°C./min.) (° C.) (min.) (MPa) (MPa) (MPa) (%) T²/Y Drawing Formingproperty Example 1 A 8 30 180 500 0.25 180 — — 200 105 — 22.5 381 9.512.5 ◯ according to 2 B 8 30 180 500 0.25 180 — — 240 130 — 22.0 44310.0 12.0 ◯ this 3 C 8 30 180 500 0.25 180 — — 250 140 — 21.0 446 11.012.0 ◯ invention 4 D 8 30 180 500 0.25 180 200 0.5 270 155 190 20.0 47011.5 11.5 ◯ 5 B 8 30 180 500 0.25 180 — — 240 130 165 22.0 443 10.0 12.0◯ 6 B 8 30 50 400 120 50 — — 155 85 — 26.0 283 8.5 14.0 ⊚ 7 B 200 5 180500 0.25 180 — — 280 165 — 22.5 475 12.0 13.0 ◯ 8 B 200 5 50 400 120 50— — 160 90 — 27.0 284 9.0 15.0 ⊚ 9 A1 8 30 180 500 0.25 180 — — 255 140— 21.5 464 11.0 12.0 ◯ 10 A2 8 30 180 500 0.25 180 — — 260 143 — 23.0473 12.0 12.5 ◯ 11 A3 8 30 180 500 0.25 180 — — 267 150 — 24.0 475 12.513.5 ⊚ Comparative 12 E 8 30 180 500 0.25 180 200 0.5 190 100 — 20.0 3619.0 9.5 ◯ Example 13 F 8 30 180 500 0.25 180 — — 180 130 — 12.0 249 6.07.5 X 14 G 8 30 180 500 0.25 180 — — 185 90 — 20.0 380 8.5 11.0 ◯ 15 H 830 180 500 0.25 180 — — 200 100 — 19.0 400 9.0 9.0 X 16 I Casting wasimpossible 17 J 8 30 180 500 0.25 180 — — 205 100 — 20.0 420 9.0 9.5 ◯18 K 8 30 180 500 0.25 180 — — 230 130 — 17.0 407 10.0 7.0 X 19 L 8 30180 500 0.25 180 — — 195 95 — 20.0 400 9.0 9.0 X 20 M 8 30 180 500 0.25180 — — 180 95 — 21.0 341 7.0 10.0 ◯ 21 N 8 30 180 500 0.25 180 — — 235140 — 16.0 394 10.0 7.0 X 22 O 8 30 180 500 0.25 180 — — 250 160 — 17.0391 6.0 5.5 X 23 P 8 30 180 500 0.25 180 200 0.5 240 150  25 22.0 38410.0 8.5 ◯ 24 Q 8 30 180 400 120 50 — — 200 90 — 26.0 444 8.5 12.0 ⊚ 25R 8 30 180 500 0.25 180 — — 270 160 — 16.0 456 10.0 6.0 X 26 S 8 30 180500 0.25 180 — — 280 165 — 16.5 475 11.0 6.0 X 27 U 8 30 180 500 0.25180 — — 190 90 — 19.0 401 9.0 8.5 ◯ 28 V 8 30 180 500 0.25 180 — — 280170 — 19.0 461 9.5 8.5 X 29 W 8 30 180 500 0.25 180 — — 190 95 — 20.0380 9.0 8.0 ◯ 30 X 8 30 180 500 0.25 180 — — 195 100 — 20.0 380 9.0 8.0◯

[0104] Having described our invention as related to the presentembodiments, it is our intention that the invention not be limited byany of the details of the description, unless otherwise specified, butrather be construed broadly within its spirit and scope as set out inthe accompanying claims.

What is claimed is:
 1. An aluminum alloy sheet material, comprising 2.6%by mass or more and less than 3.5% by mass (% by mass is simply denotedby % hereinafter) of Si, 0.05 to 0.5% of Mg, 0.5% or more and less than1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0% of Fe,with the balance of Al and unavoidable impurities.
 2. The aluminum alloysheet material according to claim 1, further containing a componentoriginating from scraps of an aluminum alloy in at least a part of thesheet material.
 3. The aluminum alloy sheet material according to claim1, wherein concentrations of Si, Mn and Fe, when they are represented byA%, B% and C%, respectively, satisfy conditions as shown by thefollowing formula: (0.015×A+0.15×B+0.03×C)≦0.445, andwherein a densityof precipitates with an average diameter of 100 μm or more is 2precipitates/cm² or less.
 4. The aluminum alloy sheet material accordingto claim 1, wherein tensile strength and 0.2% proof stress, when theyare represented by T (MPa) and Y (MPa), respectively, satisfy conditionsas shown by the following formula: T² /Y≧350.
 5. The aluminum alloysheet material according to claim 1, wherein 0.2% proof stress is 100MPa or less.
 6. The aluminum alloy sheet material according to claim 1,wherein 0.2% proof stress after baking of a coating is higher by 30 MPaor more than 0.2% proof stress before baking.
 7. A method for producingthe aluminum alloy sheet material according to claim 4, comprising:melting and casting an aluminum alloy which comprises 2.6% or more andless than 3.5% of Si, 0.05 to 0.5% of Mg, 0.5% or more and less than1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0% of Fe,with the balance of Al and unavoidable impurities; hot-rolling the castaluminum alloy after applying homogenizing treatment; cold-rolling therolled aluminum alloy, to form a sheet thereof with a prescribedthickness; and subjecting the sheet to heat-treatment by holding thesheet at a temperature of 450° C. or more for a time period of 120seconds or less, and cooling to a temperature of 100° C. or less at acooling speed of 100° C./min or more.
 8. The method according to claim7, wherein the aluminum alloy sheet material further contains acomponent originating from scraps of an aluminum alloy in at least apart of the sheet material.
 9. The method according to claim 7, whereinwith respect to the aluminum alloy sheet material, concentrations of Si,Mn and Fe, when they are represented by A%, B% and C%, respectively,satisfy conditions as shown by the following formula:(0.015×A+0.15×B+0.03×C)≦0.445, anda density of precipitates with anaverage diameter of 100 μm or more is 2 precipitates/cm² or less.
 10. Amethod for producing the aluminum alloy sheet material according toclaim 5 comprising: melting and casting an aluminum alloy whichcomprises 2.6% or more and less than 3.5% of Si, 0.05 to 0.5% of Mg,0.5% or more and less than 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% ofZn, and 0.3 to 2.0% of Fe, with the balance of Al and unavoidableimpurities; hot-rolling the cast aluminum alloy after applyinghomogenizing treatment; cold-rolling the rolled aluminum alloy, to forma sheet thereof with a prescribed thickness; and subjecting the sheet toheat-treatment by holding the sheet at a temperature of 300° C. or moreand 420° C. or less for a time period of 30 minutes or more, and coolingto room temperature at a cooling rate of 60° C./min or less.
 11. Themethod according to claim 10, wherein the aluminum alloy sheet materialfurther contains a component originating from scraps of an aluminumalloy in at least a part of the sheet material.
 12. The method accordingto claim 10, wherein with respect to the aluminum alloy sheet material,concentrations of Si, Mn and Fe, when they are represented by A%, B% andC%, respectively, satisfy conditions as shown by the following formula:(0.015×A+0.15×B+0.03×C)≦0.445, anda density of precipitates with anaverage diameter of 100 μm or more is 2 precipitates/cm² or less.
 13. Amethod for producing the aluminum alloy sheet material according toclaim 1, comprising: melting and casting an aluminum alloy whichcomprises 2.6% or more and less than 3.5% of Si, 0.05 to 0.5% of Mg,0.5% or more and less than 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% ofZn, and 0.3 to 2.0% of Fe, with the balance of Al and unavoidableimpurities, wherein a cooling rate for solidifying a molten liquid isadjusted to 50° C./sec or more by continuous cast-rolling, in themelting and casting step.
 14. The method according to claim 13, whereinthe aluminum alloy sheet material further contains a componentoriginating from scraps of an aluminum alloy in at least a part of thesheet material.
 15. An aluminum alloy sheet material, comprising 2.6% bymass or more and less than 3.5% by mass of Si, 0.05 to 0.5% of Mg, 0.5%or more and less than 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to 1.6% of Zn,and 0.3 to 2.0% of Fe, and comprising at least one selected from thegroup consisting of 0.01 to 0.2% of Cr, 0.01 to 0.2% of Zr, 0.01 to 0.2%of V, and 0.01 to 0.2% of Ti, with the balance of Al and unavoidableimpurities.
 16. The aluminum alloy sheet material according to claim 15,further containing a component originating from scraps of an aluminumalloy in at least a part of the sheet material.
 17. The aluminum alloysheet material according to claim 15, wherein concentrations of Si, Mn,Fe, Cr, Zr and Ti, when they are represented by A%, B%, C%, D%, E% andF%, respectively, satisfy conditions as shown by the following formula:{0.015×A+0.15×B+0.03×C+0.60×(D+E)+0.50×F}≦0.445, andwherein a density ofprecipitates with an average diameter of 100 μm or more is 2precipitates/cm² or less.
 18. The aluminum alloy sheet materialaccording to claim 15, wherein tensile strength and 0.2% proof stress,when they are represented by T (MPa) and Y (MPa), respectively, satisfyconditions as shown by the following formula: T ² /Y≧350.
 19. Thealuminum alloy sheet material according to claim 15, wherein 0.2% proofstress is 100 MPa or less.
 20. The aluminum alloy sheet materialaccording to claim 15, wherein 0.2% proof stress after baking of acoating is higher by 30 MPa or more than 0.2% proof stress beforebaking.
 21. A method for producing the aluminum alloy sheet materialaccording to claim 18, comprising: melting and casting an aluminum alloywhich comprises 2.6% or more and less than 3.5% of Si, 0.05 to 0.5% ofMg, 0.5% or more and less than 1.2% of Cu, 0.6 to 1.5% of Mn, 0.5 to1.6% of Zn, and 0.3 to 2.0% of Fe, and which comprises at least oneselected from the group consisting of 0.01 to 0.2% of Cr, 0.01 to 0.2%of Zr, 0.01 to 0.2% of V, and 0.01 to 0.2% of Ti, with the balance of Aland unavoidable impurities; hot-rolling the cast aluminum alloy afterapplying homogenizing treatment; cold-rolling the rolled aluminum alloy,to form a sheet thereof with a prescribed thickness; and subjecting thesheet to heat-treatment by holding the sheet at a temperature of 450° C.or more for a time period of 120 seconds or less, and cooling to atemperature of 100° C. or less at a cooling speed of 100° C./min ormore.
 22. The method according to claim 21, wherein the aluminum alloysheet material further contains a component originating from scraps ofan aluminum alloy in at least a part of the sheet material.
 23. Themethod according to claim 21, wherein with respect to the aluminum alloysheet material, concentrations of Si, Mn, Fe, Cr, Zr and Ti, when theyare represented by A%, B%, C%, D%, E% and F%, respectively, satisfyconditions as shown by the following formula:{0.015×A+0.15×B+0.03×C+0.60×(D+E)+0.50×F}≦0.445, anda density ofprecipitates with an average diameter of 100 μm or more is 2precipitates/cm² or less.
 24. A method for producing the aluminum alloysheet material according to claim 19 comprising: melting and casting analuminum alloy which comprises 2.6% or more and less than 3.5% of Si,0.05 to 0.5% of Mg, 0.5% or more and less than 1.2% of Cu, 0.6 to 1.5%of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0% of Fe, and which comprises atleast one selected from the group consisting of 0.01 to 0.2% of Cr, 0.01to 0.2% of Zr, 0.01 to 0.2% of V, and 0.01 to 0.2% of Ti, with thebalance of Al and unavoidable impurities; hot-rolling the cast aluminumalloy after applying homogenizing treatment; cold-rolling the rolledaluminum alloy, to form a sheet thereof with a prescribed thickness; andsubjecting the sheet to heat-treatment by holding the sheet at atemperature of 300° C. or more and 420° C. or less for a time period of30 minutes or more, and cooling to room temperature at a cooling rate of60° C./min or less.
 25. The method according to claim 24, wherein thealuminum alloy sheet material further contains a component originatingfrom scraps of an aluminum alloy in at least a part of the sheetmaterial.
 26. The method according to claim 24, wherein with respect tothe aluminum alloy sheet material, concentrations of Si, Mn, Fe, Cr, Zrand Ti, when they are represented by A%, B%, C%, D%, E% and F%,respectively, satisfy conditions as shown by the following formula:{0.015×A+0.15×B+0.03×C+0.60×(D+E)+0.50×F}≦0.445, anda density ofprecipitates with an average diameter of 100 μm or more is 2precipitates/cm² or less.
 27. A method for producing the aluminum alloysheet material according to claim 15, comprising: melting and casting analuminum alloy which comprises 2.6% or more and less than 3.5% of Si,0.05 to 0.5% of Mg, 0.5% or more and less than 1.2% of Cu, 0.6 to 1.5%of Mn, 0.5 to 1.6% of Zn, and 0.3 to 2.0% of Fe, and which comprises atleast one selected from the group consisting of 0.01 to 0.2% of Cr, 0.01to 0.2% of Zr, 0.01 to 0.2% of V, and 0.01 to 0.2% of Ti, with thebalance of Al and unavoidable impurities, wherein a cooling rate forsolidifying a molten liquid is adjusted to 50° C./sec or more bycontinuous cast-rolling, in the melting and casting step.
 28. The methodaccording to claim 27, wherein the aluminum alloy sheet material furthercontains a component originating from scraps of an aluminum alloy in atleast a part of the sheet material.